1. Field of the Invention
In general, the present invention provides dielectric interconnect structures and methods for forming the same. Specifically, the present invention provides an interconnect structure having a noble metal layer that is formed directly on a modified dielectric surface for applications such as Back End of the Line (BEOL) applications.
2. Related Art
Recently, noble metals such as Ruthenium (Ru) have emerged as an alternative liner material for Copper (Cu) integration for multiple reasons. For example, Ru deposition can be done by both Chemical Vapor Deposition (CVD) and Atomic Layer Deposition (ALD) techniques. Moreover, Cu has good adhesion to Ru. In addition, a Ru—Cu system is thermodynamically stable and has been reported to be immiscible. Still yet, Ru does not oxidize easily and has a fairly low bulk resistivity. The low resistivity of Ru is an important feature for it to enable direct electroplating of Cu.
Some advantages of adopting noble metals for Cu interconnect applications include the following: (1) better technology extendibility vs. current Physical Vapor Deposition (PVD) Tantalum-Nitride (Ta(N)) technology; (2) conformal deposition from ALD and CVD; (3) capable for Cu direct plating; (4) better electrical performance; and (5) thinner liner layer results in more Cu volume. Unfortunately, despite excellent adhesion strength between Cu and Ru, experimental results revealed poor adhesion between the Ru to dielectric interface. It is likely that Ru, a noble metal, bonds weakly with Carbon (C) and Oxygen (O). This could be a fundamental problem with deposition of Ru directly onto a dielectric substrate. Because of the poor Ru/dielectric adhesion issue, wafer peeling problems were observed during Cu electroplating and CMP, thus inhibiting adoption of this metallization scheme into manufacturing. Referring now to FIG. 1, a table 10 of adhesion energy (J/m2) for various interfaces is depicted. As shown, PVD of Cu on Ru, plated Cu on Ru, Ru on TaN, and PVD of Cu on Ta all exhibit high adhesion energy (e.g., >20 J/m2). However, noble metal to dielectric interfaces such as Ru on dense dielectric, and Ru on porous dielectric exhibit low adhesion energy (e.g., <3 J/m2).
Heretofore, attempts have been made at solving the aforementioned noble metal to dielectric interface adhesion issue. Referring to FIGS. 2A and 2B, two such approaches are shown. Specifically, FIG. 2A shows a dielectric interconnect structure 26 having a noble metal layer 16 (e.g., Ta). However, in order to achieve sufficient adhesion, between noble metal layer 16 and exposed dielectric layer 14, a glue layer 12 was required at all noble metal to dielectric interfaces. This included both horizontal and vertical surfaces of trenches 20A-20B and via 22. Moreover, the dielectric interconnect structure 12 of FIG. 2A applied glue layer 12 along a horizontal interface 18 between via 22 and internal metal layer 24. FIG. 2B shows dielectric interconnect structure 26 in which glue layer 12 is similarly applied on all interfaces between noble metal layer 16 and exposed dielectric layer 14 (e.g., including both horizontal and vertical surfaces of trenches 20A-20B). However, dielectric interconnect structure 26 lacks glue layer 12 along interface 18 between via 22 and internal metal layer 24. The attempts shown in FIGS. 2A-2B both suffer from disadvantages including requiring glue layer 12 to be present along all noble metal to dielectric interfaces.
In view of the foregoing, there exists a need for a solution that solves at least one of the problems/disadvantages of the existing art.